Cryogenic mediums, such as liquid oxygen, liquid nitrogen, liquid argon, liquefied natural gas (LNG), etc., are materials commonly used in industry. They have lower working temperatures and are usually stored in cryogenic vessels in liquid form. For example, the working temperature of liquid nitrogen is generally around −196° C. In the course of filling a cryogenic liquid medium from a bulk supply tank into a cryogenic vessel, the medium will vaporize continuously, resulting in pressure in the vessel rising. Such pressure rising causes the pressure difference between the bulk supply tank and the inside of the vessel, decreasing or even vanishing, so that the filling process cannot continue. Moreover, the over-high pressure in the vessel will hide some safety troubles.
Hence, filling with gas-let-out is usually adopted. As shown in FIG. 1, an existing cryogenic vessel 1 is usually provided with an inlet pipe 2 and an exhaust pipe 3. During the filling process, liquid or liquefied medium is filled into the vessel through the inlet pipe 2 while the vapor of the medium exhausts through the exhaust pipe 3 to reduce the pressure within the vessel, so as to maintain a stable pressure difference between the bulk supply tank and the inside of the vessel. In this way, however, some medium will be wasted in vapor form.
In practice, the cryogenic medium stored in a cryogenic vessel is usually in a gas-liquid equilibrium state. Thus, the filling rate of liquid within the vessel needs to be controlled during the filling process. In the prior art, an overflow pipe 4 is commonly arranged on the vessel 1. The overflow pipe 4 is opened during the filling process. When liquid begins to flow out from the overflow pipe 4, it means that the vessel reaches the designed filling rate. At this time, valves for the bulk supply tank and for pipe(s) on the vessel need to be respectively and manually turned off, so as to stop filling. In this way, however, some medium will be wasted in liquid form.
The cryogenic medium is usually obtained through various complicated processes, which consume a large amount of additional energy and money. In the existing filling manner, the medium discharged from the exhaust pipe 3 and the overflow pipe 4 will be wasted inevitably. Accordingly, not only the environment will be contaminated but also the resources will be wasted. Additionally, there will be hidden safety troubles if the wasted medium is not handled properly. Therefore, how to prevent the medium from being wasted during the filling process is a problem demanding prompt solution.
Furthermore, the existing filling manner requires operators to focus their attention on opening and closing the corresponding valves of pipes and pipelines in time. If, for example, the overflow pipe 4 is forgotten to be opened during the filling process, the liquid within the vessel might exceed the safe liquid level, thereby causing hazards, such as pressure holding, or even vessel explosion, etc.